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<a name="PCH-Target"></a>
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<a name="Parameters-for-Precompiled-Header-Validity-Checking"></a>
<h3 class="section">18.27 Parameters for Precompiled Header Validity Checking</h3>
<a name="index-parameters_002c-precompiled-headers"></a>

<dl>
<dt><a name="index-TARGET_005fGET_005fPCH_005fVALIDITY"></a>Target Hook: <em>void *</em> <strong>TARGET_GET_PCH_VALIDITY</strong> <em>(size_t *<var>sz</var>)</em></dt>
<dd><p>This hook returns a pointer to the data needed by
<code>TARGET_PCH_VALID_P</code> and sets
&lsquo;<samp>*<var>sz</var></samp>&rsquo; to the size of the data in bytes.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fPCH_005fVALID_005fP"></a>Target Hook: <em>const char *</em> <strong>TARGET_PCH_VALID_P</strong> <em>(const void *<var>data</var>, size_t <var>sz</var>)</em></dt>
<dd><p>This hook checks whether the options used to create a PCH file are
compatible with the current settings.  It returns <code>NULL</code>
if so and a suitable error message if not.  Error messages will
be presented to the user and must be localized using &lsquo;<samp>_(<var>msg</var>)</samp>&rsquo;.
</p>
<p><var>data</var> is the data that was returned by <code>TARGET_GET_PCH_VALIDITY</code>
when the PCH file was created and <var>sz</var> is the size of that data in bytes.
It&rsquo;s safe to assume that the data was created by the same version of the
compiler, so no format checking is needed.
</p>
<p>The default definition of <code>default_pch_valid_p</code> should be
suitable for most targets.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fCHECK_005fPCH_005fTARGET_005fFLAGS"></a>Target Hook: <em>const char *</em> <strong>TARGET_CHECK_PCH_TARGET_FLAGS</strong> <em>(int <var>pch_flags</var>)</em></dt>
<dd><p>If this hook is nonnull, the default implementation of
<code>TARGET_PCH_VALID_P</code> will use it to check for compatible values
of <code>target_flags</code>.  <var>pch_flags</var> specifies the value that
<code>target_flags</code> had when the PCH file was created.  The return
value is the same as for <code>TARGET_PCH_VALID_P</code>.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fPREPARE_005fPCH_005fSAVE"></a>Target Hook: <em>void</em> <strong>TARGET_PREPARE_PCH_SAVE</strong> <em>(void)</em></dt>
<dd><p>Called before writing out a PCH file.  If the target has some
garbage-collected data that needs to be in a particular state on PCH loads,
it can use this hook to enforce that state.  Very few targets need
to do anything here.
</p></dd></dl>

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